Arrangement for controlling the operation of a high-frequency power amplifier

ABSTRACT

An arrangement for controlling the operation of a high-frequency power amplifier includes a high-frequency power amplifier connected to a forward line and a control, and an attenuator connected to the input side thereof. A sampler and a detector are connected to a feedback line between the output side and the input side of the high-frequency power amplifier. An amplifier is connected to the feedback line on the input side of the detector, the gain of the latter amplifier being of the same order of magnitude as the attenuation provided by the attenuator.

BACKGROUND OF THE INVENTION

The invention relates to a method and an arrangement for controlling theoperation of a high-frequency power amplifier.

In GSM transmitters, for instance, specifications place rigidrestrictions also on the operation of the transmitter as well as onswitching on or off the transmission power. When the transmission poweris switched off at a GSM transmission, it should be possible to reducethe transmission power during idle time slots between frames by at least70 dB, in practice by 80 dB, which can be realized by decreased gain andby using RF switching means providing an attenuation of about 40 dB, inaddition to the 40 dB obtained by the control of the amplifier. Oneproblem with the previous solutions is that the dynamic range ofdetector means is only about 40 dB.

In some methods and arrangements according to the prior art, thetransmission power is switched off by using a switching means positionedin a power control loop on the input side of an amplifier, whereby thesignal path breaks, however, and the detector output remains floating ina way. This generates a control signal undefined in its details in acontrol means of the input side of the amplifier, which in turn causesproblems, i.e. practically a control error in a situation when thetransmission power shall be switched on again. A control error may alsocause a decrease in attenuation when the power is switched off. Thisrestricts the permitted maximum gain between the detector and thecontrol means as well, which maximum gain determines in turn theaccuracy of the output power in an ON state.

In another known embodiment, a switching means is positioned in anantenna line outside a power control loop, which requires, however, anamplifier and an RF switch with a higher power, which leads to biggerpower losses.

It is also known from the prior art to use a logarithmic RF rangeamplifier and detector to expand the dynamic range of the detector, butthe component in question is an expensive hybrid component and thus notnecessarily a suitable choice always.

From European Patent Application 0 135 154 is known an apparatus forcontrolling transmission power, but no reference is made therein tobringing an amplifier to an OFF state. The objective of the apparatusdisclosed in that publication is to minimize variations in loop gaincaused by the non-linearity of the power amplifier. The EP publicationrelates to controlling DC gain and by no means to controlling RF gain orRF attenuation, which is the case in the present invention. In thesolution disclosed in the EP publication, the control of a power controlloop comes from inside the loop.

THE INVENTION

The object of the present invention is to set forth a novel method andarrangement for controlling the operation of a high-frequency poweramplifier, which avoid the problems associated with the known solutions.

This object is achieved by means of the method according to theinvention, which is characterized in that the high-frequency poweramplifier is brought to the OFF state without breaking the signal pathby attenuating the signal to be inputted to the input side of thehigh-frequency power amplifier by a desired attenuation and byamplifying the signal of the feedback line by a desired gain. Thearrangement according to the invention is characterized in that anamplifying means is connected to the feedback line on the input side ofthe detector, the gain of which means is of the same order of magnitudeas the attenuation of the attenuation means.

The method and arrangement according to the invention are based on theidea that both attenuation and gain are supplied to the power controlloop without breaking the signal path, due to which the detector meansdoes not react to switching off the transmission power in a detrimentalmanner, which caused control error in the previous solutions.

Several advantages are achieved by means of the solution according tothe invention especially therein that the power control loop does notbreak, not even when the power is switched off, due to which a narrowerfrequency spectrum and a faster reaction to reswitching the gain areprovided. In the solution of the invention, the properties of thehigh-frequency power amplifier are better than in the known solutions,both during gain and when the power is switched on or off. The newsolution provides a smaller power loss than a solution the switchingmeans of which is in an antenna line. The new solution also provides amore accurate output power than a solution the switching means of whichis on the input side of the power amplifier.

The method comprises inputting a signal to be amplified to ahigh-frequency power amplifier in a forward line, generating a samplesignal from the forward line on the output side of the high-frequencypower amplifier to a feedback line, controlling the high-frequency poweramplifier via the feedback line on the basis of the sample signal by acontrol means connected to the input side of the high-frequency poweramplifier and bringing the high-frequency power amplifier to an OFFstate controlled by a control signal.

The arrangement according to the invention comprises a high-frequencypower amplifier connected to a forward line, a control means and anattenuation means connected to the input side of the high-frequencypower amplifier and a sampling means and a detector means connected to afeedback line between the output side and input side of thehigh-frequency power amplifier. The forward line and the feedback lineform a kind of a power control loop, by means of which the power of atransmitter is connectable to an antenna.

The present solution relates especially to multichannel radiotransmitters and how to switch on the transmission power of ahigh-frequency power amplifier of a radio transmitter and particularlyhow to switch off the transmission power, i.e., how to bring it to anOFF state. One example of radio transmitters is a base station radiotransmitter of a GSM mobile telephone network utilizing a TDMA system,the high-frequency power amplifier of which transmitter amplifies thesignals to be received from a modulator before these are inputted to anantenna.

BRIEF DESCRIPTION OF THE DRAWING

In the following, the invention will be described in more detailreferring to the attached drawings, in which

FIG. 1 shows a block diagram of an arrangement according to theinvention,

FIG. 2 shows an embodiment of the position of an amplifying means of afeedback line.

DETAILED DESCRIPTION

The arrangement of FIG. 1 comprises a power control loop constituted bya forward line A and a feed-back line B. The arrangement comprises ahigh-frequency power amplifier 1 connected to the forward line A, acontrol means 2 and an attenuation means 3 connected to the input sideof the high-frequency power amplifier 1. The control means 2 may berealized by means of a volt age-controlled attenuator (VCA), forinstance, and the attenuation means 3 may in turn be realized forexample by means of switches and resistances in such a way that eitheran attenuation of 40 dB or a very small attenuation is achieved by theattenuation means. Indication P(IN) represents the input side, to whicha signal to be amplified comes from a modulator of a transmitter andindication P(OUT) represents an antenna line starting from the outputside of the amplifier. In addition, the arrangement comprises a samplingmeans 4 and a detector means 5 connected to the feedback line B betweenthe output side and the input side of the amplifier. The sampling means4 may preferably be constituted by a directional coupler, such as amicrostrip directional coupler, by which from an output signal of theamplifier is generated a sample signal 6 proportional to the strength ofthe output signal. The sample signal 6 is detected by the detector means5, which may be constituted by a rectifier implemented by means ofdiodes, for instance.

To the feedback line B on the input side of the detector 5 is connectedan amplifying means 7, the gain of which is of the same order ofmagnitude, preferably very exactly the same, as the attenuation of theattenuation means 3 on the input side of the high-frequency poweramplifier 1. The preferred embodiment of FIG. 1 shows that theattenuation means 3 not breaking the signal path is connected betweenthe control means 2 and the high-frequency power amplifier 1 and thatthe amplifying means 7 of the feedback line B is connected between thedirectional coupler acting as the sampling means 4 and the detectormeans 5. Referring further to FIG. 1, the arrangement also comprises acontrol unit 8, a summer 9 and a low-pass filter 10.

The attenuation means 3 not breaking the signal path may be connectedalternatively in front of the control means 2, in which case the controlmeans 2 and the attenuation means 3 would thus be in opposite order inFIG. 1.

The method for controlling the operation of a high-frequency poweramplifier comprises inputting a signal to be amplified to ahigh-frequency power amplifier 1 in a forward line A, generating asample signal from the forward line A on the output side of thehigh-frequency power amplifier 1 to a feedback line B by means of asampling means 4. The method further comprises detecting the samplesignal by a detector means 5, summing the detected sample signal to areference signal 11 to be obtained from a control unit or actuatingmeans 8, low-pass filtering the summation signal 12 by a low-pass filter10 and gain, if necessary. The method also comprises controlling thegain of the high-frequency power amplifier 1 on the basis of thedetected, summed and filtered sample signal by a control means 2connected to the input side of the high-frequency power amplifier. Whenthe power is switched off, the method also comprises bringing thehigh-frequency power amplifier 1 to an OFF state controlled by controlsignals 13 and 14, which control signals 13 and 14 are generated in thecontrol unit 8. The high-frequency power amplifier is brought to the OFFstate, without breaking the signal path, by attenuating the signal to beinputted to the input side of the high-frequency power amplifier 1 by anattenuation means 3 with a desired attenuation and by amplifying thesignal of the feedback line B with a desired gain and preferablyexpressly as much as the signal of the input side was attenuated. Inthis case, the attenuation to which the forward line A of the input sideof the high-frequency power amplifier 1 shall be exposed issubstantially equal to the gain to which the feedback line shall beexposed, thanks to which the detector means 5 omits to react toswitching off the power better and better and is thus capable ofavoiding control errors.

The voltage-controlled control means 2 performs an attenuation of 40 dBand the attenuation means 3 performs another attenuation of still 40 dB,thanks to which the signal to be connected is attenuated by 80 dB, whichis enough. In order not to exceed the dynamic range of the detector 5, asignal passing simultaneously to the detector 5 in the feedback line isamplified with 40 dB by an amplifying means 7, i.e. an amplifier servingsaid feedback line. As the amplifying means 7 of the feedback line isused a switched gain amplifier with a gain of 40 dB, for instance. Theamplifying means 7 is active only in an OFF state of power switchingwhen the power of the high-frequency amplifier itself is switched off.Correspondingly, as the attenuation means 3 is used a switchedattenuator with an attenuation of 40 dB, for instance, which attenuatoris active only in an OFF state when the power of the high-frequencypower amplifier itself is switched off. In a preferred embodiment, theattenuation of the forward line A and the gain of the feedback line Bare switched on by the common control unit 8 according to FIG. 1, andexpressly by the same control unit 8 by which the reference signal 11 isinputted to the summer 12, making a solution possible which isstructurally the simplest and the easiest to implement. The control unit8 constitutes an external control means 8 with respect to the loop, bywhich means RF attenuation and RF gain are controlled.

In a preferred embodiment, separate detector means are used fordetecting separate power ranges. These separate detector means havesensitivities deviating from each other, the first detector means beingused for detecting an OFF state and the second detector means being usedfor detecting an ON state. The sensitivities are selected in such a waythat the detector means which is active in an OFF state, i.e. when poweris switched off, is more sensitive.

FIG. 2 shows an embodiment of the position of the amplifying means 7 ofthe feedback line. In FIG. 2, the input side IN is connected to thesampling means 4 of FIG. 1 and the output side OUT is connected to thedetector 5 of FIG. 1. In the embodiment of FIG. 2, the arrangementcomprises a first switching means 51 connected in series with theamplifying means 7 of the feedback line, and the arrangement comprisesfurther a second and a third switching means 52 and 53 and a conductormeans 54 between them. The second and the third switching means 52 and53 can be connected in series either with the conductor means 54 or withthe first switching means 51 and the amplifying means. The switchingmeans 51 to 53 are arranged under common control, the upper position ofFIG. 2 showing a normal situation with no gain supplied to the feedbackline. In a situation with the switches 51 to 53 in the lower position, again of about 40 dB is supplied to the feedback line, i.e. as much asthe forward signal is attenuated by the attenuation means 3 of FIG. 1.As far as choice of components is concerned, the solution of FIG. 2 is apreferred embodiment, since switching means at fair cost are usedtherein. The typical attenuation capacity of the switching means of SPDTtype shown in FIG. 2 is about 30 dB at GSM frequencies.

In FIG. 2, with the switch 51 in open position, i.e. in the upperposition, the amplifier is connected to a terminal 55, which may beimplemented by means of a resistance, for instance. The advantage isthen achieved that the input of the amplifier 7 does not remain openwhen the switch 51 is open. Accordingly, the amplifying means 7 is onits input side connectable to the input IN via the switches 51 and 52when they are in the lower position, or alternatively, the amplifyingmeans 7 is connectable via the switch 51 to the terminal, in this caseto the resistance 55, when the switches 51 and 52 are in the upperposition.

The solution according to FIG. 2 is presented only as an example, i.e.as one preferred embodiment, and it is clear that the solution of FIG. 2also has several alternative embodiments, such as the one in which thetwo signal paths between the input and output shown in FIG. 2 maycomprise a separate directional coupler and/or a detector means.

In one preferred embodiment, different amplification values are providedby changing the sample signal 6 to be taken from the output side of thehigh-frequency power amplifier 1 and coming to the amplifying means 7.This is preferably made possible by means of at least two separatedirectional couplers contained in the input side of the amplifying means7, or by a corresponding means, the output signals of which deviate fromeach other.

Though the invention has been described above with reference to theexamples according to the attached drawings, it is clear that theinvention is not restricted to them, but it can be modified in many wayswithin the scope of the inventive idea set forth in the attached claims.

I claim:
 1. A method for controlling the operation of a high-frequencypower amplifier, comprising the steps of:(a) inputting a signal to beamplified, to an input side of a high-frequency power amplifier, in aforward line providing a signal path; (b) generating a sample signalfrom the forward line, on an output side of said high-frequency poweramplifier, to a feedback line as a signal of the feedback line; (c)controlling the high-frequency power amplifier via said feedback line onthe basis of said sample signal, by a control connected to the inputside of the high-frequency power amplifier; and (d) bringing the poweramplifier to an OFF state control signals without breaking the signalpath, by:(i) operating an attenuator for attenuating the signal beinginputted to the input side of the high-frequency power amplifier by adesired attenuation, and (ii) operating a feedback line amplifier foramplifying the signal of the feedback line by a desired gain.
 2. Themethod of claim 1, wherein:the attenuation and gain provided in step (d)are substantially equal in magnitude.
 3. The method of claim 1,wherein:step (d) includes providing said control signals to saidattenuator and to said feedback line amplifier by a control unit servingboth said attenuator and said feedback line amplifier in common.
 4. Themethod of claim 1, wherein:step (d)(i) includes causing the feedbackline amplifier to provide different amplification values by changingsaid sample signal of said feedback line as inputted to said feedbackline amplifier.
 5. An arrangement for controlling a high-frequency poweramplifier, comprising:a high-frequency power amplifier having an inputside and output side, said high-frequency power amplifier beingconnected in a forward line and providing with said forward line asignal path; a control means connected to the input side of thehigh-frequency power amplifier; an attenuation means connected to theinput side of the high-frequency power amplifier for providing anattenuation, without breaking said signal path, when actuated; afeedback line serving said control means; a sampling means connected tosaid feedback line and arranged to provide a signal for said feedbackline which is proportional to signaling carried by said forward line onthe output side of said high-frequency power amplifier; a detector meanshaving an input side and an output side and being connected to saidfeedback line for detecting signalling carried by said feedback linebetween said sampling means and said control means; a feedback lineamplifier connected to said feedback line between the input side of saiddetector means, for providing a gain, when actuated which is of the sameorder of magnitude as said attenuation; and means for actuating saidattenuation means and said feedback line amplifier so as to respectivelyprovide the respective attenuation and gain at a same time.
 6. Thearrangement according to claim 5, wherein:said attenuation means iseffectively connected to said forward line between said control meansand said high-frequency power amplifier; said sampling means comprises adirectional coupler; and said feedback line amplifier is effectivelyconnected to said feedback line between said directional coupler andsaid detector means.
 7. The arrangement according to claim 5,wherein:said control means is effectively connected to said forward linebetween said attenuating means and said high-frequency power amplifier;said sampling means comprises a directional coupler; and said feedbackline amplifier is effectively connected to said feedback line betweensaid directional coupler and said detector means.
 8. The arrangementaccording to claim 5, further comprising:a first switching meansconnected in series with said feedback line amplifier to said feedbackline; a second switching means; a third switching means; a conductorconnecting said second and third switching means; said second and thirdswitching means being switchable between being connected in serieseither with said conductor means, or with said first switching means andsaid feedback line amplifier.
 9. The arrangement according to claim 8,further comprising:a terminal; said feedback line amplifier, arranged tobe switched off at an input side thereof by said first switching meansand connected to said terminal.
 10. The arrangement of claim 9,wherein:said terminal comprises a resistance.